A more thorough explanation:

The Court of the Marshalsea was a court that moved around with the king and had jurisdiction over certain cases within 12 miles of the king's residence. It was also known as the Court of the Steward and Marshal.

The Court's steward and marshal acted as judges and heard criminal cases and common pleas of debt, covenant, and certain trespasses. However, it could not try newer forms of action such as assumpsit and trover.

The Court's migratory nature made it inconvenient for litigants, and it was abolished in 1849. Its once general jurisdiction had passed to the court of King's Bench.

For example, if someone committed a crime within 12 miles of the king's residence, they would be tried in the Court of the Marshalsea. However, if someone wanted to sue someone else for a newer form of action like assumpsit, they would have to go to the court of King's Bench instead.